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It was believed to be the first time he had taken up the issue of sex abuse with a senior member of his staff since his election on 13 March.

Archbishop Muller is head of the Congregation for the Doctrine of the Faith.

This department includes the office of the "promoter of justice", or sex crimes prosecutor, which investigates cases of sexual abuse and decides if priests are to be defrocked.

Pope Francis said the department should continue to "act decisively as far as cases of sexual abuse are concerned,"

He urged: "promoting, above all, measures to protect minors, help for those who have suffered such violence in the past (and) the necessary procedures against those who are guilty," a Vatican statement said.

It said the Pope wanted Catholic bishops around the world to promote and put into place "directives in this matter which is so important for the witness of the Church and its credibility".

Victims’ groups say there is much still to be discovered about how the Church behaved in the past and want more bishops who were aware of abuse to be held responsible.